Since
routing protocols need to adjust to topology change, an overhead is incurred due
to the exchange of routing messages. For variable topology networks, such an
overhead may impose a significant limit on scalability and effective capacity.
For example, it has been noted from measurement data that in certain modern
networks (e.g. a portion of the U.S. Air Force network), such overheads
constituted 80% of the total traffic carrying capacity. Thus, it is important
to understand how the overhead scales for various protocol-design choices.

We
developed an information-theoretic framework for the characterization of bounds
on the least overhead incurred by various classes of routing protocols under a
uniform traffic pattern. The key departure point of the new framework is to
treat the state (e.g. link state, node location, hybrid of both) as a random
variable that exhibits random changes. The minimum protocol overhead is related
to the minimum amount of information (i.e. effort) needed to identify the
current state of the system, possibly within a distortion bound. The various
state changes are derived from the probability distribution describing the
cause of dynamism, e.g. the nodes mobility pattern. Thus the protocol overhead
problem is brought into an information theoretic framework, and terms like
entropy rate now yield new practical design guidelines and basic limits on the
best possible protocol design. For example, we can now characterize the highest
possible effective capacity of a network, by subtracting the lowest capacity
deficit among all possible protocol designs.

We have also
considered the routing protocol overhead problem from a different angle that
has not been considered before in the literature. That is, we took into account
the interdependence between the communication pattern, in terms of the
distribution of number of hops between source destination pairs, and the
routing overhead. Interestingly, it turns out that reactive routing protocols
can operate efficiently for asymptotically large networks (even with an
infinite number of nodes) if the traffic is sufficiently localized
statistically. We have analytically characterized the sufficient conditions and
validated them through extensive simulations of realistic protocol
implementations.

Presentations:

"Entropy
Measures of Routing: Towards a First Law of MANET Info-dynamics," DARPA ITMANET workshop March 7, 2006:.pdf